Intended for healthcare professionals

Clinical Review Snapshots from the decade of the brain

Brainy mind

BMJ 1998; 317 doi: (Published 19 December 1998) Cite this as: BMJ 1998;317:1693
  1. Richard Gregory, emeritus professor.
  1. Department of Experimental Psychology, University of Bristol, Bristol BS8 1TN

    Editorial by Martyn and pp  p 1693-708 We have all been struck by the spooky question: Is your sensation of green like my green? For how can we compare sensations —or qualia, as philosophers call them —>of colours, tastes, or sounds? Our green qualia may be different (and in cases such as colour anomalies must be different), though we all call grass green and assume we all see the same.

    Summary points

    • Sensations of consciousness —qualia —are created by the brain

    • Qualia are psychologically projected into the external world of objects

    • Perceptions are predictive hypotheses, based on knowledge stored from the past

    • As perceptions may be 90% memory, how is the present moment distinguished from memory and anticipation?

    • Qualia may be evoked by afferent sensory stimuli to avoid confusion with the past and future by flagging the present moment

    Where do sensations come from?

    The primary question is whether the brain receives or makes sensations. When we look at grass: is the sensation of green picked up by the eyes, from light reflected from the grass, or is the sensation, the qualia of green, created in our brains? It is now as certain as anything —as Isaac Newton appreciated three centuries ago — that light itself has no colour. Light evokes colour in suitable eyes and brains, which is very different. And violins have no sounds without ears and brains to create sound qualia. Recently the brain scientist Semir Zeki located colour creating cells in the brain (in the visual area of the striate cortex V4).

    One can imagine a bunch of interacting robots getting on fine without any awareness of qualia; but surely they wouldn't spend hours looking at pictures, or listening to Beethoven. This is just how behaviourist psychologists a few years ago described us —as lacking consciousness, or qualia of …

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